It is therefore a first object of the invention to provide an improved package, in which there is an adequate filling of the areas between the pads below a chip, particularly in case of a relatively large chip surface and a relatively thin top layer of the frame.
It is a second object of the invention to provide a method of manufacturing the package.
The first object is achieved in that:                the frame contact pads each comprise a first patterned layer and a second patterned layer, which second layer has the surface that is exposed outside the encapsulation,        at least a portion of the frame contact pads in the die attach area has a first patterned layer with a first pattern that comprises at least one flange/lead that is outside the second patterned layer when seen in perpendicular projection of the first layer on the second layer.        
The second object is achieved as claimed in the independent method claim.
In the package of the invention, the frame has a first patterned layer and a second patterned layer. The first patterned layer comprises a flange. When placing a die on the frame with regular patterns, there is most probably a frame contact pad with a flange that is only partially covered by the die. This flange can be used for the provision of a wirebond to said frame contact pad. The second patterned layer, of which a surface constitutes a terminal of the package, is however located inside the die attach area. In other words, the density of terminals is optimized, while the functionality of a regular pattern is maintained.
It is believed suitable that the frame has a uniform design, in which any pads in the die attach area have the same size and shape as outside the die attach area. This would substantially reduce the costs of the frame, since one frame design can be used for several applications. Additionally, the subdivision of the die pad in such plurality of pads of uniform size most efficiently solves any problems with the removal of moisture from the die attach adhesive. Such solutions contribute to meeting the MSL-tests in the qualification of products.
It is observed that it is not technically necessary to have a regular pattern throughout the frame. In other words, the frame contact pads with the flange may be present in a limited area of the frame only, and the regularity of patterns is interrupted. Nevertheless the extension of the regular pattern throughout the frame is believed to be most beneficial.
It is further observed for clarity that the term ‘frame’ refers here to a carrier with the first and second patterned layers. In a most suitable embodiment, the frame is of the kind disclosed in WO-A 2003/85728; in this embodiment, the second patterned layer is only patterned after the provision of the encapsulation. Thereafter, the frame is in fact subdivided into a plurality of individual frame contact pads. The mechanical integrity is then maintained in that the frame contact pads are anchored or embedded within the encapsulation and/or another filling layer. This frame of WO2003/85728 is suitably used with a very thin intermediate layer. It has the advantage of inherent solder adhesive layers, which are also used as etch masks. The manufacture by means of etching results in an anchoring of the pads into the compound and die attach adhesive through the non-planarity/flatness of the side faces of the die pads.
It will be understood that it is not necessary that all frame contact pads have the same shape, in order to arrive at a regular pattern. In fact, there may be a unit that is regularly repeated, which unit may comprise several different patterns. Alternatively and/or additionally, there may be a first and a second area comprising different frame contact pads with different patterns, which first and second area are laterally spaced apart.
The flange is in the context of the present application a conductor with a lateral extension resulting in a non-square shape. The shape in top view may be rectangular or otherwise. Good results are expected from a tripod or Y-shape, which allows a very regular division—uniform density—of the pads in the frame. It further can be etched adequately. Other shapes include T-shapes, L-shapes and X-shapes. S-, 2- and Z-shapes and derivatives thereof with other internal angles between the legs of the basic shape are also interesting options.
The advantage of such lateral extension is at least two-fold: first, it can be used as an interconnect track with low resistance. Such a interconnect track is particularly useful in case of a multichip package. The low ohmic connection may then be made with a plurality of tracks which are mutually connected, for instance with wirebonds. Another useful feature of the interconnect track is that its lateral extension allows the provision of more wirebonds to a single pad. Secondly, it may be used for rerouting, particularly for rerouting to a position within the die attach area. The latter function may reduce the overall package size.
A most advantageous modification hereof is that the lateral extension is present in the upper layer, while in a corresponding portion of the lower layer a pad with a standard shape is defined. Then, the resulting packages may have a standard and accepted footprint. A standard shape is herein for instance a square, a round or a somewhat rectangular shape, with a pitch of for instance 0.4, 0.5, or 0.8 mm.
Suitably, in combination herewith, the upper layer of the frame has a small thickness, for instance in the order of 10 to 100 microns, more suitably in the order of 20 to 60 microns. Then the lateral extensions will not reduce an average distance between neighboring pads in the frame (also known as pitch).
Particularly with the embodiment of a regular Y-, T-, I- or L-shaped patterns, spaces between these patterns tend to get the form of channels. It is therefore understood to be advantageous to fill the channels, and particularly those in the die attach area with an adhesive, instead of with molding compound.
One suitable embodiment of an adhesive is an adhesive applied at the back side of the die. Such adhesive is known in the art as a Wafer Back Coating, or a Wafer Back Laminate, as commercially available from chemical suppliers such as Henkel. The Wafer Back Laminate as currently available allow filling of the channels, if the thickness of the first patterned layer is less than 40 microns, more suitably less than 30 microns. Evidently, this depends to a certain extent on several factors such as:                the number of channels (and particularly the area filled relative to the total die attach area,        the width of the channel (which could make the adhesive flow outside the die attach area)        the further development of Wafer Back Laminate        
Another suitable alternative to provide the adhesive is the use of a paste to the frame. Such a paste can be provided with screenprinting or a similar technique. The paste appears less suitable in case the channel width is reduced to less than 5 or 10 microns.
A most suitable alternative to provide the adhesive is the use of a two-layered type adhesive, that is available for die to die bonding with wires that need protection. On application, the first layer (adjacent to the die) is harder than the second layer (exposed). A gentle heating step allows filling of the spaces. A further curing step (possibly simultaneous with the overmoulding) would make this very hard.
In an even further embodiment, the chip is assembled to the frame in a die attach area, which die attach area has an inner area and a further area. The die attach adhesive is applied in the inner area, while leaving the further area free; and the encapsulation is applied so as to fill the further area, therewith mechanically anchoring the chip. In this embodiment, the area in which the die attach adhesive is applied is reduced, in comparison to packages with a conventional die attach pad extending in the complete die attach area. The further area, particularly an area near to the edge of the chip, is then filled during the provision of the encapsulation. The further area that is filled with molding compound may be ring-shaped. Alternatively, it may comprise a plurality of areas within the die attach area, each of those extending to an edge of the die attach area. The number of areas could be two or more, for instance four.